Description Of Main Circuit Operation - Hitachi RAS-14EH1 Service Manual

DESCRIPTION OF MAIN CIRCUIT OPERATION

MODEL RAS-14EH1
1. Reset Circuit
Voltage supply to
pin 2 of IC521
Voltage at pin 7
of microcomputer
The reset circuit initializes the microcomputer program when power is ON or OFF.
Low voltage at pin 7 resets the microcomputer and Hi activates the microcomputer.
When power "ON" 5V voltage rises and reaches 4.4V, pin 1 of IC521 is set to "Hi". At this time the microcomputer
starts operation.
When power "OFF" voltage drops and reaches 4.2V, pin 1 of IC521 is set to "Low". This will RESET the
microcomputer.
5V
2
R552
1
5
3
IC521
0V
Fig. 1-1
Voltage
5.0V
Reset release at 4.4V
Voltage
5.0V
Fig. 1-2
– 30 –
NORMAL : HI
RESET
7
Microcomputer
Power "OFF"
Power "ON"
Reset enter at 4.2V
: LO
RES